For gaming this is death were it's not bandwidth that kills you, it's latency.
I wonder how this could work in the "internet of tubes" analogy to explain to people?
You want hot water from the tap. If you haven't used it in a while or have poorly insulated pipes it could take seconds or even minutes before hot water starts flowing through the tap after you've turned the knob.
Traffic. While a section of highway (say a 3 lane x 40' section) may see 30 cars every minute, a particular car that just started 60 miles away and traveling at 60mph is still going to take an hour to arrive. Even though tons of other traffic is going through constantly the particular vehicle (message) is still in transit.
Echos are probably easy to explain this with, and are directly analogous to the sort of ping-pong, back-and-forth that network communication uses. You shout out a message and it can only travel at the speed of sound. It'll take seconds to cross the ravine and the same time to return to you. Shout 10 messages and 10 messages return in the same order all delayed by the same amount.
I have a number of technical friends, but also a lot of non-technical friends. Being a nerd, however, I tend to bring up technical topics amongst my non-technical friends more often than is fair. I've found that many of our CS topics (networking, OS, performance, security, etc.) have good physical analogs to at least convey a 10,000' view. Often (like latency) there are some almost perfect analogies that everyone has experienced or witnessed. I'm not turning them into programmers, but they'll understand the terms better.
Pretty simple. Water takes time to flow from one end of the pipe to the other. If you are trying to fill a huge tank, doesn't really matter how long it takes the water to get to you. If you are trying to fill a hundred tiny cups, it does matter because you are shutting the tap off and on again pretty frequently.
Wireless hardware shares a chunk of the spectrum, much like cell phones share a chunk of the spectrum. So a node is not always transmitting the way a full-duplex ethernet connection is. Your packets wait for their slot to open up and then they are transmitted. The same happens on the way back. So the throughput can be extremely high but the latency can be murderous at the same time. And that's assuming the packet made it in one piece and did not have to be re-transmitted, in which case the lag will be even longer.
I hope that explains it clearly enough.
IOW, if it's not clear, the speed of sound in glass (assuming the marbles are made of glass).
Look at http://eyes.nasa.gov/dsn/dsn.html, for Voyager the latency would be 0.74 days. For the Mars Reconnaissance Orbiter it would be 6.6 minutes.
Someday people might play live action video games with someone on Mars with very little latency, but right now it's not even theoretical without a wormhole through space/time.